Known sliding gratings such as those which are used for cooling cement clinker and other, pourable burnt material comprise a plurality of rows, running transversely with respect to the longitudinal and advancement direction of the cooling unit, of grating plates which are alternately stationary and moved back and forth in the conveying direction, the grating plates arranged one behind the other overlapping one another in an imbricated manner. The bed of material which is to be cooled moves over the upper side of the plates and has a wearing effect on the same. It is known (EP-C 337383; EP-A 537523; U.S. Pat. No. 5,174,747), for the upper side of the plates to be provided, in the material-receiving surface over which the bed of material slides, with depressions, in which material particles are held and in which cooling-air-outlet openings open out. This arrangement has the advantage that the cooled material held in the depressions protects the grating-plate region located therebeneath against the thermal and wearing action of the bed of material sliding over it, and that the cooling air is well distributed by the material located in the depressions. Since the front plate section is at particular risk of wear, it is provided, essentially over its entire width, with one or more such depressions. In contrast, the rear section is subjected to thermal action to a lesser degree because it is overlapped to a periodically alternating extent by the grating plate arranged behind. In order that this plate which is arranged behind can slide over the plate in front without being spaced apart therefrom to a pronounced extent, the surface of said rear section is usually designed to be more or less smooth and parallel to the direction of relative movement. It is referred to as the sliding surface hereinbelow.
The known plates provided, in the front section, with depressions on top have a cooling-air-supply space which is connected to the cooling-air-outlet openings and has a cooling-air-supply opening which is connected to the associated grating-plate carrier. The latter is a hollow carrier which is assigned to each row, the cavity of which is used for cooling-air supply, and on which the grating plates are mounted with their rear region projecting forwards.
In order to be able to hold some of the material better, the depressions in the material-receiving surface are designed with steep delimiting surfaces and to be as deep as possible in comparison with the plate height provided. This means that there is only a small cross-section remaining for the cooling-air-supply space located therebeneath, as a result of which the supply of cooling air to those cooling-air-outlet openings which are arranged further towards the front in the plate and for which the cooling requirement is particularly high is poorer than for those openings which are arranged further towards the rear. Although the cross-section of the cooling-air-supply space could be increased by selecting a larger plate height, this increases the material requirement, which determines costs. Moreover, the higher plates then no longer match the hitherto conventional, lower plates.